I'm confused ... by second format do you mean convert the seemingly non-number value to time & then to seconds ...

Incidentally I think the answer should be 170 seconds, no ?

return 170 as integer (not time format (decimal))

A1: 2.5
B1: =INT(A1)*60+(100*MOD(A1,1))
or
B1: =(INT(A1)+(MOD(A1,1)/0.6))*60

or time format (ie result is decimal - formatted to time)

A1: 2.5 (non time)
B1: =(INT(A1)+(MOD(A1,1)/0.6))/1440
B1 Formatted as: [ss]